在.NET中，将数据从SQL传输到文件

I have to get a DataTable from SQL, and then convert it to XML (I can't use SQL XML) and save to a file. The problem is that the file is going to be 5 GB, and I don't have enough memory to download it all and convert it to XML all at once in memory. I know I should be able to use a DataReader to convert and push the data to the file stream in chunks, but I don't know how to really do this. How can I do the following?I have to get a DataTable from SQL, and then co